In order to create a magnetic field, the coils must be formed from conductive wires coated with a layer of insulating material. Any failure of this insulating material would result in short-circuiting the turns and therefore reducing the inductance of the coil.
The coils are usually formed from copper wire. Currently, the insulation of the wires is produced with thermosetting polymer materials such as polyester, polyamide, polyepoxide or polyimide varnishes, according to the specified requirements for resistance to temperature. Once the insulating wire coils have been produced, they are additionally impregnated with another layer of resin. These solutions make it possible to produce compact coils that are satisfactory for normal applications.
Aeronautical applications require optimization of these solutions in terms of mass and volume. A first way consists of optimizing the proportion of the volume of conductor to the total volume of the insulated coil. The use of copper wires with a rectangular cross section, for example, meets this objective by limiting the interstices compared with wires with a circular cross section.
However, in order to further save in weight, aluminum is used in place of copper. In fact, the use of aluminum strips for manufacturing coils combines the advantage of compact geometry and a low-density conductive material.
In addition, the use of anodizing for electrically insulating aluminum is a very mature solution that also has the advantage of having a resistance to temperature very much greater than current solutions.
Consequently, anodized aluminum coils that can be used for producing electrotechnical components are currently being sold. They are supplied to the dimensions of the component and all that remains to be done then is to integrate them in the latter with, in particular, additional impregnation with resin.
However, the use of these coils has several drawbacks:                firstly, the aluminum is immediately sealed with hot water after anodizing, which has the effect of blocking the pores of the alumina formed during anodizing and thus of reducing the adhesion properties of this surface, and therefore of reducing the service life of the component;        in addition, manufacturing the coil requires the use of an adhesive in order to bond the anodized aluminum strips to one another; the use of this adhesive introduces an additional material, the uncontrolled interface of which with the resin used for the additional impregnation in the component reduces the durability of the component.        